This invention relates to a semiconductor photodetector element suited as an image sensor in various types of image processing. In particular, it relates to a semiconductor photodetector element for use in a bar code reader and for pattern collation of plane images.
Semiconductor photodetector elements were conventionally so designed that the rows of image elements constituting a screen were scanned in one fixed direction. As a result, if a row of photodetector cells on such an element contained a defective cell, it was not possible by the element by itself to detect the error in image information caused by the output from this defective cell. For this reason, it was considered necessary in order to obtain reliable image information to output information for each screen successively to a processing system for optimization. Another disadvantage of unidirectional scanning was that the image data could be taken in only successively so that difficulties arose in the case of a moving image or a pseudo-stationary image because the conventional semiconductor photodetector element required external clock synchronization for scanning and one could obtain information only on such image changes restricted by this clock synchronization.
In the signal amplification circuit of a conventional semiconductor photodetector element, furthermore, since the signal reading line was shared by different image element rows, a reset input in synchronism with the external clock was necessary for each scan.